When A Star Falls
by Grimarisen22
Summary: After having a fight with her twin brother Dipper Pines, Mabel runs away towards a mountain, to get away from him and the harsh reality. Upon reaching the mountain, she accidentally stumbles down a deep hole. Who knew that underneath the mountain, lies a great mystery?
1. Chapter 1

**Chapter 1:**

Mabel stirs, her eyes opening up slowly. Her brain is throbbing a lot. She sits up slowly and looks around, adjusting to her surroundings. It's a little dark. Suddenly, she remembers the whole ordeal. The fight, running away to a mountain with Dipper trailing behind her and then the fall. She accidently fell into a hole. She should've cracked hundreds of bones, heck, she shouldn't even be alive! Her body aches a little, but otherwise okay.

 _How is that possible?_ She then looks at the ground, realizing why the impact didn't kill her. Underneath her is a bed of golden flowers.

"They're so pretty..." Mabel whispers, awestruck. Then, she snaps up.

"No! This is no time for flower viewing, Mabel, you have to get out of here!" she scolds herself and gets up. Dusting her clothes, she looks up but regrets it. The light was blinding her vision. Mabel looks away to readjust her eyes. After a few moments, she again gazes up.

With a hand to shield her eyes a little, Mabel tries to see something, anything other than the light.

 _Maybe Dipper's there?_

"Dipper! Dipper, can you hear me? Dipper!" Mabel cries out, her eyes squinting. She looks away, her vision blurry.

 _Where's Dipper? Why isn't he responding? Can't he hear me? Will I get out of here?_

A thousand thoughts swarmed through her mind, all of them were negative ones, but she pushed them aside. Even if he can't hear her, he'll definitely find a way to rescue her. Dipper's the smart twin, he can get out in any situation.

She thought about the last conversation that they had, Mabel can't help but feel depressed. She remembers their fight that they had. It's still fresh in her mind.

" _I can't believe you agreed to that! Everything's going away and now you too?!"_

" _Mabel, things change. We can't stay like this forever"_

" _It all has to end someday.."_

She didn't realize that she's been crying until now, with the tears welling up in her eyes, making her vision blurry. Mabel has never felt more alone like this. Might as well explore the place. She again checked her surroundings and spotted a path. Without giving a second thought, she took that path.

Upon going further along the path, an entrance appeared. Mabel hesitated, casting a glance back at the place behind her. With a deep breath she went in.

"Howdy!"

* * *

 **Hi, everyone! My name's Ivy and this is pretty much the first story that I'm publishing here in . Please go easy on me as this is my first time writing a fanfiction. I have soooo many ideas about so many fanfics. This is one of them. I had this Gravity Falls x Undertale idea ever since I finished the game. I'm so so very sorry for my grammar and mistakes! English is not my native language, I'm still learning. But criticism is appreciated! The next chapter will come up this week I promise, and it will be bigger than this one!**


	2. Chapter 2

**A/N: A long chapter! Sweet! I hope you like it. Also, read the A/N after the story. It's important.**

* * *

Chapter 2:

Mabel jumped up, startled. She glanced all around her till her eyes casted downwards. There, situated in the middle of a patch of grass, was a pretty yellow flower with eyes, and a mouth that curled upwards in a small smile. Mabel stared wide-eyed at it.

 _Did that flower just smile and greet her?_

"I'm Flowey, Flowey the Flower! Nice to meet you!" It beamed at her. _It's a talking flower. OH MY GOD IT'S A MAGICAL TALKING FLOWER._

Mabel kneeled down, facing the flower with a big grin that almost reached her eyes. "Hi Flowey, I'm Mabel! Mabel the uh…human? Yeah! Mabel the Human!" she replied, proudly. Flowey simply smiled more.

"Howdy, Mabel! A human? Golly! We don't have much humans coming here; you must be new to the Underground," It glanced at her with an unknown glint in its eyes.

"Yeah, I am actually! I just fell down a hole and ended up here and I don't know how to get out," Mabel frowned. She sneaked a look behind her, where the entrance was. If only she had a rope or maybe her grappling hook, she could have got out of the place, but unfortunately, she dropped the grappling hook while running away.

Mabel sighed and looked at the flower with hopeful eyes, "Can you help me?"

"Sure I can! But first, someone has to teach you how everything works here. Welp, I guess lil' old me will have to do!" It winked at her. Wow, that's one cheeky flower.

Mabel felted something within her grow warm, she looked down, perplexed, and gasped. A red shaped heart was glowing inside of her. She put her hands on the heart, but nothing happened. It just continued shining.

"Wh-what's happening?" she asked, shakily. Flowey answered by chuckling at her.

"Relax, that's your SOUL", it said matter-of-factly. "Your soul starts of weak, but it will grow strong gradually if you earn LV."

Mabel gave a confused look while Flowey explained further about it, "And what is this LV? Well, it's LOVE!"

Flowey grinned, "Do you want some LOVE? Of course you do!" Mabel giggled to herself; all of this seemed like a Disney tale to her. Maybe Flowey's going to break off into a song?

"I will share some of my LOVE with you!" white shaped ovals appeared, floating over her. "Here, LOVE is collected by, little white 'friendliness pellets'!"

Flowey called out,"Grab as many of them as you can, Mabel!" Mabel stood up and extended her arms out to catch them. The pellets fell down onto her. She caught them but for some reason, collecting them made her whole body weaken.

Mabel's stumbled back, her knees feeling wobbly until they gave up causing her to kneel on the ground again. Her chest, where her SOUL is located, began to ache and the red glow was fading out.

 _Oh no._

In an instant she looked at Flowey, feeling utterly betrayed. "Why?" she mumbled.

Dropping the false façade, the flower revealed its true self. With its evil smile coiling up and empty, hollow eyes boring at her.

"YOU IDIOT," it bellowed.

"IN THIS WORLD," Flowey continued, "ITS KILL OR BE KILLED." Pellets like the previous ones circled around Mabel.

"Now, DIE", maniacal laughter echoed through the whole area. Panicked, Mabel tried to look for an exit, but to no avail, the pellets were closing in on her.

"Wait, no! Stop!" Mabel begged causing more laughter.

"Dipper!" she cried out in a last resort, but of course, Dipper doesn't come out to rescue her. She's stuck here.

 _Maybe it's for the best?_ Mabel thought, _maybe she deserved this for being so selfish and spoiled?_

All hope was gone for Mabel, until the pellets stopped and disappeared.

 _What?_ Mabel frowned, confused. Flowey mirrored the same expression as her, only more angry than puzzled. Something blazed from the corner of her eye. Mabel watched as a fireball knocked Flowey out, causing the flower to spiral away from her line of vision.

Someone new stood in front of her now. The person was tall and had goat-like features, with horns, small fangs and long, droopy ears. She wore a simple purple and white robe. Round concerned eyes were looking down at her.

Finally, she spoke in a gentle voice,"Are you okay my child?"

Mabel simply gaped at her. The person reached out but she backed away. She can't afford to believe anyone here anymore. It was stupid of her to trust that evil flower. She won't let her guard down.

The woman sighed, "Oh what a sinful creature, frightening such a small girl."

She smiled at Mabel, "Do not be scared, my dear. I am Toriel, caretaker of the Ruins," Toriel reassured her.

"I come over to this place to check if anyone fell down the hole. You are indeed the first human that fell down here for a very long time..." she looked wistful, as if she remembered something, but then cleared her throat, "Come along, I will guide you through the Ruins," Toriel stretched her arm out, indicating that she hold her hand.

Mabel hesitated, she still doubted Toriel. Still, there's something about Toriel that makes Mabel want to believe her. Trusting her guts, she accepted Toriel's hand and together they walked out of the place and into the Ruins.

* * *

Mabel didn't expect the Ruins to look this well off and in place. The whole place was colored purple. The walls, pillars and stairways were made of stone. Piles of red leaves were found everywhere. The air felt warm, for some reason. Mabel could occasionally see weird creatures from the corners of her eyes gazing at her but when she gazed back, they disappeared. Toriel didn't let go of her hand or even loosened the grip. She started explaining about the different puzzles located in the ruins and how to solve them by demonstrating one of them while they reached a hallway.

"Okay now you try, I marked the ones that you need to turn on so it should be easy," Toriel told her, smiling.

"Okay!" Mabel grinned and steps forward, feeling excited. Indeed, the puzzle was easy. Way too easy. She switched the ones that were marked. After finishing the puzzle, Mabel went back to Toriel.

"All done! It was pretty easy. Can I solve something that's harder?" Mabel asked. Toriel chuckled in response.

"Of course, my child! There are more difficult puzzles ahead of us that need solving."

"You know, I have a name. Call me Mabel!" Mabel offered, smiling.

"Okay, Mabel dear," Toriel replied, patting her cheek gently. "Now let's move along!"

Going further were more puzzles. Mabel wanted to solve them but Toriel said the answers before she even started them. Mabel whined a lot after each puzzle, saying that she should do them by herself but Toriel still helped her, being concerned for her safety.

Finally they reached another room but to Mabel's surprise, there were no switches or rocks or spears. Only a mere dummy at the side.

Toriel glanced at Mabel, "As you're a human, there will be some monsters that will attack you," she stated, gravely.

"For that, you need to be ready when that occurs, but you shouldn't worry about it. When you engage with a monster, they will want to fight you. Instead of fighting them, you should act in a certain way so that they won't attack you. You're very smart and strong-willed, Mabel. You will have to stall them until I'm there to stop the fight, okay?" Toriel squeezed Mabel's hand reassuringly. Mabel nodded in understanding.

"Now try practicing with the dummy."

* * *

After the practice and more puzzle-solving, Toriel had to leave to run for an errand. She gave Mabel a cellphone to call her if there's any trouble. Mabel wondered how a cellphone actually worked in the Underground since there's no signal. She wanted to ask Toriel about this but decided against it. _Maybe it's a magical phone?_

 _If that's the case than maybe she can call her family?_

"Now Mabel, please do not explore the place by yourself. There's still more puzzles that I haven't explained yet, okay?" she gripped her shoulder gently, and looked at Mabel with stern eyes.

 _Not a chance_

"Okay!" Mabel said with a fake smile.

When Toriel left, Mabel immediately whipped out the phone and started dialing her brother's number.

 _No answer_

Mabel frowned and called her brother again but nobody picked up. She tried calling the Mystery Shack, but nobody responded. With a sigh, she placed her phone back in her skirt pocket and trudged forward to explore more of the vast place of the Ruins.

* * *

"Oooh, candy!" Mabel exclaimed when she saw what was on the bowl. There was a little note beside the bowl, 'Take only one, please'. Mabel took a candy and ate it, but wasn't satisfied with only one. She looked at the bowl warily, tempted to take another one. Finally she gave in and got one more.

"Curse my sweet tooth!" she cried out dramatically, sighing, she popped the candy into her mouth.

Mabel yelped as her phone started ringing. She answered her phone, "Hello?"

"Hello, Mabel! This is Toriel. I was wondering… which one do you prefer, Cinnamon or Butterscotch?" Toriel asked at the other end of the line. Mabel took a moment to think. Both of them are amazing but Mabel doesn't know which one to choose.

"Hmmm", she drawled out, "I don't know, anything works for me!" Mabel admitted truthfully.

"Oh okay. I understand." Toriel replied and hanged up. Weird.

* * *

Mabel kept stumbling onto different kinds of monsters after that. Usually with Froggits. Some of them were friendly and guided Mabel the way while others wanted to fight her. Taking Toriel's advice, Mabel started to talk to the Froggits by complimenting them, like saying, "You have nice eyes" or "I like how you say ribbit, it's very cute". The Froggits blushed (Yes, they blush, its adorable) and spared her. There were other monsters like Whimsuns, but they started crying and then left before she even uttered a word. There were also these Veggie monsters that shoved vegetables in her mouth. Each time she ran into a fight, her chest started glowing and her soul got visible. She found that very odd.

On her way to another room, her path was blocked by a ghost. They were sleeping on a pile of red leaves. Mabel really didn't want to step on them so she asked the ghost to move.

"Umm, hey ghost! Can you step out of the path? I need to cross the other side", Mabel said, she peered down at the ghost.

"ZZZZZZZZZZZZZZZZZZZZZzzZZZZZZZZZZZZZZZZZ," the ghost replied.

"Uh…" she blinked.

"ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ."

 _Does the ghost think this is a cartoon show? Why is it saying 'zzzz' out loud?_

Mabel huffed, "You know, that's not very convincing."

The ghost finally got up, well, floated up; huge tears started flooding down from their eyes.

 _GHOSTS CAN CRY?_

"Aw don't cry! You're such a nice ghost! Why are you crying? Here look!" Mabel started making weird faces. That earned a small smile from the ghost, but it's still not enough.

Mabel said a small joke that she heard from Grunkle Stan. Finally, the ghost cheered up.

"Heh" the ghost said, "I wanna sure you a trick, here look..." the ghost's tears went upwards, making a hat.

"It's called, Dapper Blook. What do you think..?" they seemed nervous.

Mabel giggled, "That was really cool!"

The ghost looked hopeful, "Really? Wow..." they mumbled. "I think this is my lucky day, that I've met a person who appreciated that..."

"Aw! Well this is my lucky day too! I never knew I'd run into a nice ghost. Say, what's your name? I'm Mabel. Let's be friends!" Mabel said excitedly.

"Hello, Mabel. I'm Napstablook," they smiled, "well I should be going. It was nice meeting you," and with that they disappeared.

* * *

"Why are you here? Are you okay? Did you get hurt? Why did I leave you alone, it's so foolish of me!" Toriel rambled out checking for any signs of injuries. Feeling overwhelmed with all the unnecessary worry, Mabel laughed out loud, "its okay! I didn't get hurt or die."

Toriel sighed tiredly, "Preparing for the surprise made me forget…"she trailed off, realizing that she spoke out loud.

"A surprise? Oh my God!" Mabel started jumping up and down.

"Oh well, I guess I can't keep it a secret now," Toriel smiles, looking at her, "Come along my child, I have a big surprise for you," she grabs her hand and lets her into a small home.

The home seemed cosy and small. It reminds Mabel of her home. The air was warm and filled with the smell of cinnamon.

"Surprise! I made a butterscotch-cinnamon pie for you just for today!" She beamed at her, "But, that's not all, come," she leaded Mabel to the right entrance, a long hallway appeared with 3 rooms. She stopped at the first room.

"This is your room! I hope you like it," she patted Mabel's head affectionately.

She surprises Toriel by hugging her, "Thank you so much!" Mabel said grinning.

Toriel hugged back, "You're welcome," she whispered, smiling. "Make yourself at home, I'll be right back with the pie," Toriel finished and then scurried off.

Mabel lets out a yawn. All this walking and exploring made her tired. She entered the room and sprawled herself on the bed.

 _A small nap will work_

That was the last thought she had before she drifted to sleep.

* * *

 **A/N: Whew! That took forever to write. Partly because I've been really busy lately. School's just around the corner. Anyway enough of that, let's get to the important bits. This fanfic is going to take a real different turn than the game. The story, the characters, the ending. EVERYTHING. I really want this fanfic to stand out than the other gravity falls x undertale ones. Also, this fic is a Mabel-centric fic. Meaning no mystery twins solving the mountain together. But, that doesn't mean you won't get to read about Dipper! I'm going to switch POVs, to get the idea on what's happening on the outside world, how Dipper and the rest are coping with Mabel's disappearance. There will be a maximum of 2 of it. The REAL story's going to begin in the next chapter. Expect updates in the next week, though I'm not sure which day. Maybe Friday? Idk.**

 **Now about the author! I cannot wait for tomorrow because I'm FINALLY gonna watch Star Wars: The Force Awakens! (WOOOOOOOOOOO) I'm a HUGE Star Wars fan. I've been avoiding spoilers since the movie released and so far, I've been successful. Can't wait for the movie! THE HYPE IS REAL.**

 **-Ivy**


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